Disk types in Managed Service for Greenplum®

Managed Service for Greenplum® allows you to use network and local storage drives for database clusters. Network drives are based on network blocks, which are virtual disks in the Yandex Cloud infrastructure. Local disks are physically located on the cluster servers.

When creating a cluster, you can select the following disk types for data storage:

• Network HDDs (network-hdd): Most cost-effective option for clusters that do not require high read/write performance.

• Network SSDs (network-ssd): Balanced solution. Such disks are slower than local SSD storage, but, unlike local disks, they ensure data integrity if Yandex Cloud hardware fails.

• Non-replicated SSDs (network-ssd-nonreplicated): Network disks with enhanced performance achieved by eliminating redundancy.

  The storage size can only be increased in 93 GB increments.

• Ultra high-speed network SSDs with three replicas (network-ssd-io-m3): Network disks with the same performance characteristics as non-replicated ones. This disk type provides redundancy.

  Such disks can be increased in size only in 93 GB increments.

  Access to high-performance SSDs is available on request. Contact support or your account manager.

• Local SSDs (local-ssd): Disks with the best performance.

  The size of such a storage can be increased:

  • For Intel Cascade Lake: Only in 100 GB increments.

  • For Intel Ice Lake: In 368 GB increments only.

  Note

  For clusters with hosts residing in the ru-central1-d availability zone, local SSD storage is not available if using the Intel Cascade Lake platform.

In a Managed Service for Greenplum® cluster, the type of disks for master hosts and segment hosts may differ.

Specifics of local SSD storageSpecifics of local SSD storage

Local SSDs do not provide fault-tolerant storage and impact the cost of the entire cluster: you are charged for a cluster with this type of storage even if it is stopped. You can find more information in the pricing policy.

Disk space managementDisk space management

If any host storage is more than 95% full, the cluster will switch to read-only mode automatically, all DBs get the DEFAULT_TRANSACTION_READ_ONLY = TRUE setting through the ALTER DATABASE query.

In this mode, the INSERT, DELETE, or UPDATE queries result in an error.

Monitoring the transition to read-only modeMonitoring the transition to read-only mode

To monitor storage usage on cluster hosts, configure alerts in Yandex Monitoring:

1. Go to the folder page and select Monitoring.

2. Select Managed Service for Greenplum®.

3. Create a notification channel.

4. Create an alert with the following properties:

   1. Metric: Set the following metric parameters:

      • Cloud

      • Folder

      • Managed Service for Greenplum® service

      • Managed Service for Greenplum® cluster ID

        You can get the cluster ID with a list of clusters in the folder.

      • disk.free_bytes label

   2. Condition: Set the Less than or equals condition for free disk space utilization percentage to trigger the alert:

      • 95% of the storage size for Alarm
      • 90% of the storage size for Warning

   3. Advanced settings:

      • Aggregation function: Minimum (minimum metric value for the period).
      • Evaluation window: Preferred metric update period.

   4. Add the previously created notification channel.

Recovering a cluster from read-only modeRecovering a cluster from read-only mode

If the cluster switched to read-only mode:

• Increase the storage capacity so that it exceeds the threshold value. Yandex Cloud will then disable read-only mode automatically.

• Disable read-only mode manually and free up storage space by deleting some data.

  Alert

  When doing so, make sure the amount of free disk space never reaches zero. Otherwise, since the fail-safe mechanism is disabled, Greenplum® will crash and the cluster will stop operating.

To disable read-only mode manually, contact support or follow the steps below:

1. Connect to the database in any appropriate way.

2. Open a transaction and run the following command inside it:

   SET LOCAL transaction_read_only TO off;
   

3. As part of the same transaction, delete the data you do not need using the DROP or TRUNCATE operators. Do not use the DELETE operator, as it marks rows as deleted but does not physically delete them from the database.

4. Commit the transaction and restart all connections to the database.

For example, if your database contains a table called ExcessDataTable1 that you no longer need, delete it using the following transaction:

BEGIN;
SET LOCAL transaction_read_only TO off;
DROP TABLE ExcessDataTable1;
COMMIT;

Greenplum® and Greenplum Database® are registered trademarks or trademarks of VMware, Inc. in the United States and/or other countries.